1. Field of the Invention
The invention relates to an apparatus for the thermal tempering of panes of glass, having two blow boxes arranged opposite one another, each having a plurality of blow nozzles.
2. Background of the Prior Art
Tempering devices of this type are primarily used for the manufacture of safety glass for motor vehicles. They are known in various embodiments. Thus, for example, one known blow box is made from an air distribution box, the front plate of which is provided with a plurality of air discharge openings. An example for the construction of such a blow box is shown in DE-OS 14 71 820. In order to create better conditions for the necessary flow of the air after it impinges on the hot glass panes, however, this type of blow box consisting of an air distribution box and a front plate provided with air discharge openings often has a front plate provided with nozzle pipelets between which the hot air can flow laterally. A blow box of
this type is shown, for example, in DE-AS No. 24 08 084. Other blow boxes provide projecting nozzle webs which extend laterally over the blow boxes, in which the air discharge openings are formed in the nozzle webs, and whereby the flow of the hot air takes place through the intermediate spaces between the nozzle webs. Blow boxes with this construction are described, for example, in DE-AS No. 23 33 924 and DE-OS No. 34 25 809.
It is also known to adapt the air discharge area formed by the air discharge openings or by the openings of the blow pipelets to the shape of the glass panes if the glass panes to be tempered are curved. In this way it is intended that the air discharge openings overall have the same spacing from the glass surface, and that a uniform tempering is achieved in this manner over the entire surface of the glass.
It is also known, for economic reasons, to temper the glass panes with blow boxes corresponding to their size. However, because re-equipping a tempering device by exchanging the blow boxes is a time-consuming process, in practice large blow boxes are generally used which are designed for the largest glass panes they will handle. In so doing, it is simply accepted that a portion of the compressed air for the tempering of the glass is not used when smaller glass pieces are tempered.